Feature Name | Class | Elev. meters | County | Latitude DMS | Longitude DMS |
| O'Connell School (historical) | School | 390 | Vernon | 43 41 52 N | 090 39 05 W |
| O'Connor Branch | Stream | | Richland | 43 16 15 N | 090 37 41 W |
| O'Connor Branch | Stream | | Richland | 43 16 15 N | 090 37 40 W |
| O'Day Lake | Lake | 465 | Oneida | 45 38 54 N | 089 38 35 W |
| O'Donnell Residence Hall | Building | 206 | Milwaukee | 43 02 22 N | 087 56 09 W |
| O'Dovero Farms | Locale | 418 | Ashland | 46 19 45 N | 090 36 29 W |
| O'Hara Creek | Stream | | Douglas | 46 09 29 N | 091 37 22 W |
| O'Hara Hall | Building | 196 | Milwaukee | 43 02 16 N | 087 55 36 W |
| O'Keefe Creek | Stream | | Marquette | 43 40 55 N | 089 33 16 W |
| O'Leary Lake | Lake | 183 | Grant | 42 32 27 N | 090 38 17 W |
| O'Neil Creek | Stream | | Chippewa | 44 59 54 N | 091 21 08 W |
| O'Neil Creek Cemetery | Cemetery | 293 | Chippewa | 45 01 06 N | 091 23 55 W |
| O'Neil Creek Flowage Number One | Lake | 325 | Chippewa | 45 12 06 N | 091 21 25 W |
| O'Neil Creek Flowage Number Two | Reservoir | 323 | Chippewa | 45 11 32 N | 091 21 36 W |
| O'Neil Creek Flowage Trail | Trail | 333 | Chippewa | 45 11 02 N | 091 21 41 W |
| O'Neil Flowage 0.2 | Reservoir | 324 | Chippewa | 45 11 60 N | 091 21 19 W |
| O'Neil Flowage 0.5 | Reservoir | 332 | Chippewa | 45 11 30 N | 091 21 31 W |
| O'Neil Flowage 1 E12.206 Dam | Dam | 324 | Chippewa | 45 11 60 N | 091 21 19 W |
| O'Neil Flowage 2 E12.206 Dam | Dam | 323 | Chippewa | 45 11 32 N | 091 21 36 W |
| O'Neil Ridge | Ridge | 348 | Crawford | 43 18 24 N | 090 53 12 W |
| O'Neil Ridge School (historical) | School | 344 | Crawford | 43 18 11 N | 090 52 56 W |
| O'Neill Creek | Stream | | Clark | 44 33 57 N | 090 36 15 W |
| O'Toole School | School | 307 | Lafayette | 42 32 08 N | 090 16 13 W |
| Oak Center | Populated Place | 274 | Fond du Lac | 43 39 39 N | 088 36 00 W |
| Oak Center Cemetery | Cemetery | 277 | Fond du Lac | 43 38 48 N | 088 36 03 W |
| Oak Center School (historical) | School | 268 | Fond du Lac | 43 40 06 N | 088 35 59 W |
| Oak Center School (historical) | School | 239 | Pepin | 44 35 24 N | 092 03 13 W |
| Oak Center School (historical) | School | 343 | Pierce | 44 38 44 N | 092 27 10 W |
| Oak Creek | Populated Place | 214 | Milwaukee | 42 53 09 N | 087 51 47 W |
| Oak Creek | Stream | | Milwaukee | 42 54 22 N | 087 50 31 W |
| Oak Creek Cemetery | Cemetery | 219 | Milwaukee | 42 54 07 N | 087 55 51 W |
| Oak Creek Church | Church | 225 | Milwaukee | 42 53 15 N | 087 55 57 W |
| Oak Creek East Middle School | School | 207 | Milwaukee | 42 52 35 N | 087 54 04 W |
| Oak Creek Harbor | Locale | 177 | Milwaukee | 42 50 46 N | 087 49 36 W |
| Oak Creek High School | School | 216 | Milwaukee | 42 53 15 N | 087 54 27 W |
| Oak Creek Plaza Shopping Center | Locale | 222 | Milwaukee | 42 54 07 N | 087 54 38 W |
| Oak Creek Public Library | Building | 213 | Milwaukee | 42 53 17 N | 087 54 38 W |
| Oak Forest Sanatorium | Hospital | 225 | La Crosse | 43 52 19 N | 091 13 18 W |
| Oak Glen Farm | Locale | 361 | Richland | 43 32 38 N | 090 37 40 W |
| Oak Grove | Populated Place | 263 | Dodge | 43 23 10 N | 088 44 44 W |
| Oak Grove (historical) | Populated Place | 292 | Eau Claire | 44 40 21 N | 091 36 19 W |
| Oak Grove Cemetery | Cemetery | 299 | Burnett | 45 53 28 N | 092 21 56 W |
| Oak Grove Cemetery | Cemetery | 262 | Columbia | 43 33 05 N | 089 29 28 W |
| Oak Grove Cemetery | Cemetery | 267 | Dodge | 43 23 11 N | 088 45 04 W |
| Oak Grove Cemetery | Cemetery | 363 | Dunn | 45 11 35 N | 091 55 37 W |
| Oak Grove Cemetery | Cemetery | 307 | Juneau | 44 12 36 N | 090 18 48 W |
| Oak Grove Cemetery | Cemetery | 204 | La Crosse | 43 49 11 N | 091 13 50 W |
| Oak Grove Cemetery | Cemetery | 310 | Monroe | 43 57 41 N | 090 30 24 W |
| Oak Grove Cemetery | Cemetery | 264 | Monroe | 44 03 33 N | 090 52 01 W |
| Oak Grove Cemetery | Cemetery | 317 | Polk | 45 14 48 N | 092 41 57 W |
| Oak Grove Cemetery | Cemetery | 340 | Portage | 44 27 13 N | 089 16 08 W |
| Oak Grove Cemetery | Cemetery | 232 | Racine | 42 48 55 N | 088 00 41 W |
| Oak Grove Cemetery | Cemetery | 264 | Walworth | 42 50 06 N | 088 43 22 W |
| Oak Grove Cemetery | Cemetery | 286 | Waukesha | 42 51 54 N | 088 29 14 W |
| Oak Grove Center School | School | 378 | Barron | 45 36 36 N | 091 42 15 W |
| Oak Grove Elementary School | School | 204 | La Crosse | 43 56 38 N | 091 18 04 W |
| Oak Grove Farm | Locale | 378 | Richland | 43 25 13 N | 090 38 05 W |
| Oak Grove Park | Park | 270 | Walworth | 42 34 31 N | 088 31 42 W |
| Oak Grove School | School | 182 | Brown | 44 30 09 N | 087 59 02 W |
| Oak Grove School | School | 405 | Clark | 44 50 34 N | 090 27 02 W |
| Oak Grove School | School | 334 | Crawford | 43 17 14 N | 091 00 22 W |
| Oak Grove School | School | 280 | Dane | 42 52 14 N | 089 29 57 W |
| Oak Grove School | School | 363 | Grant | 42 59 45 N | 090 28 43 W |
| Oak Grove School | School | 284 | Green Lake | 43 39 51 N | 089 03 36 W |
| Oak Grove School | School | 412 | Monroe | 43 49 26 N | 090 40 32 W |
| Oak Grove School | School | 238 | Waukesha | 42 51 24 N | 088 06 06 W |
| Oak Grove School (historical) | School | 332 | Barron | 45 16 23 N | 091 40 28 W |
| Oak Grove School (historical) | School | 240 | Brown | 44 33 33 N | 087 47 08 W |
| Oak Grove School (historical) | School | 379 | Buffalo | 44 14 23 N | 091 36 29 W |
| Oak Grove School (historical) | School | 245 | Buffalo | 44 27 49 N | 091 42 03 W |
| Oak Grove School (historical) | School | 280 | Chippewa | 44 54 04 N | 091 22 51 W |
| Oak Grove School (historical) | School | 338 | Crawford | 43 17 16 N | 091 00 21 W |
| Oak Grove School (historical) | School | 320 | Dunn | 45 05 31 N | 091 48 15 W |
| Oak Grove School (historical) | School | 317 | Eau Claire | 44 38 34 N | 091 33 16 W |
| Oak Grove School (historical) | School | 283 | Fond du Lac | 43 39 44 N | 088 48 59 W |
| Oak Grove School (historical) | School | 272 | Fond du Lac | 43 53 44 N | 088 38 54 W |
| Oak Grove School (historical) | School | 313 | Jackson | 44 22 18 N | 090 53 31 W |
| Oak Grove School (historical) | School | 214 | Outagamie | 44 18 55 N | 088 14 27 W |
| Oak Grove School (historical) | School | 258 | Pepin | 44 39 53 N | 091 54 31 W |
| Oak Grove School (historical) | School | 339 | Polk | 45 20 22 N | 092 27 19 W |
| Oak Grove School (historical) | School | 217 | Richland | 43 12 51 N | 090 13 11 W |
| Oak Grove School (historical) | School | 364 | Rusk | 45 26 41 N | 090 59 51 W |
| Oak Grove School (historical) | School | 355 | St. Croix | 44 56 58 N | 092 24 21 W |
| Oak Grove School (historical) | School | 329 | Trempealeau | 44 34 31 N | 091 10 32 W |
| Oak Grove School (historical) | School | 238 | Waupaca | 44 22 02 N | 088 46 27 W |
| Oak Grove Stock Farm | Locale | 218 | Richland | 43 12 55 N | 090 14 28 W |
| Oak Grove Town Hall | Building | 378 | Barron | 45 36 35 N | 091 42 14 W |
| Oak Hall | Populated Place | 296 | Dane | 42 57 02 N | 089 26 13 W |
| Oak Hall Cemetery | Cemetery | 318 | Dane | 42 57 04 N | 089 27 04 W |
| Oak Hill | Populated Place | 250 | Jefferson | 42 56 09 N | 088 35 12 W |
| Oak Hill Cemetery | Cemetery | 305 | Dane | 42 57 52 N | 089 37 38 W |
| Oak Hill Cemetery | Cemetery | 262 | Dane | 43 08 38 N | 089 44 19 W |
| Oak Hill Cemetery | Cemetery | 273 | Dodge | 43 26 18 N | 088 38 30 W |
| Oak Hill Cemetery | Cemetery | 257 | Jefferson | 43 10 60 N | 088 58 22 W |
| Oak Hill Cemetery | Cemetery | 268 | Jefferson | 43 11 39 N | 088 42 04 W |
| Oak Hill Cemetery | Cemetery | 461 | Lincoln | 45 24 22 N | 089 38 29 W |
| Oak Hill Cemetery | Cemetery | 267 | Marquette | 43 47 44 N | 089 26 45 W |
| Oak Hill Cemetery | Cemetery | 285 | Marquette | 43 50 52 N | 089 33 44 W |
| Oak Hill Cemetery | Cemetery | 238 | Outagamie | 44 32 44 N | 088 33 16 W |
| Oak Hill Cemetery | Cemetery | 282 | Rock | 42 42 11 N | 089 02 44 W |
| Oak Hill Cemetery | Cemetery | 256 | Sauk | 43 22 37 N | 089 37 54 W |
| Oak Hill Cemetery | Cemetery | 271 | Sauk | 43 27 60 N | 089 52 04 W |
| Oak Hill Cemetery | Cemetery | 524 | Vilas | 46 09 14 N | 089 15 22 W |
| Oak Hill Cemetery | Cemetery | 310 | Walworth | 42 36 26 N | 088 26 25 W |
| Oak Hill Cemetery | Cemetery | 271 | Waukesha | 43 04 59 N | 088 08 42 W |
| Oak Hill Cemetery | Cemetery | 261 | Winnebago | 44 04 38 N | 088 48 05 W |
| Oak Hill Cemetery | Cemetery | 237 | Winnebago | 44 11 24 N | 088 29 28 W |
| Oak Hill School | School | 309 | Polk | 45 36 47 N | 092 34 13 W |
| Oak Hill School (historical) | School | 310 | Buffalo | 44 35 41 N | 091 56 18 W |
| Oak Hill School (historical) | School | 336 | Chippewa | 45 04 24 N | 091 38 45 W |